The invention relates to conductor track structures on an electrically non-conductive supporting material and to a method for the production thereof.
Methods for producing fine, adherent conductor track structures have been disclosed in German Patent Applications DE 197 23 734.7-34 and DE 197 31 346.9 and the special issue entitled “Feinstrukturierte Metallisierung von Polymeren” [Finely Structured Metallization of Polymers], of the technical journal “metalloberfläche,” No. 11, Vol. 54 (2000), according to which non-conductive metal chelate complexes are introduced into a non-conductive supporting material. Structured metallization nuclei are then split from these metal chelate complexes using laser radiation and subsequently initiate metallization by chemical reduction in the irradiated partial areas.
Such methods can be used, for example, for producing circuit substrates made of thermoplastic materials using an injection molding process. Compared to alterative methods for producing three-dimensional injection-molded circuit substrates—so-called molded interconnect devices—these methods have the advantage that the tooling costs can be kept relatively low. Furthermore, the number of the required process steps can be reduced because the undecomposed metal chelate complex can remain in non-irradiated areas on the surface of the circuit substrate. As a result, even medium scale production becomes very economical, while a particularly fine resolution of the structure can be achieved.
These advantages are offset by the marginal thermal stability of the described metal chelate complexes with respect to the processing temperatures of modern high-temperature plastics, such as LCP. As a result, this method has limited applicability for this group of materials, which in view of the new lead-free soldering technologies is becoming ever more important. On the other hand, the metal chelate complexes have to be added in relatively large amounts to obtain sufficiently dense nucleation for rapid metallization when activated by laser irradiation. However, the high proportion of these complexes frequently affects important properties of the supporting material, e.g., its elongation at break and its impact strength.
The 1999 Activity Report of the Chair of Production Technology (LFT) of the University of Erlangen-Nürnberg describes an analogous approach in which laser radiation is used to release metallization nuclei that are not chemically integrated as described above but are physically passivated by encapsulation of metal particles. Since the encapsulated particles are significantly larger than the molecules of a typical metal chelate complex, the conflict of goals, i.e., “small admixture to the plastic—high density of nuclei after laser irradiation” leads to substantially greater problems than nucleation using metal chelate complexes that can be split by a laser.
WO 00 35 259 A2 describes a method for producing fine metallic conductor structures on an electrically non-conductive substrate. According to this method an electrically non-conductive metal complex structured with organic complexing agents is applied to, or introduced into, the substrate. The substrate is selectively subjected to UV radiation in the area of the conductor structures to be produced. As a result metal nuclei are released and the area is metallized by chemical reduction. This makes it possible to obtain fine conductor structures using a simplified and reliable method.